|Publication number||US20090105762 A1|
|Application number||US 12/287,035|
|Publication date||Apr 23, 2009|
|Filing date||Oct 3, 2008|
|Priority date||Oct 23, 2007|
|Also published as||WO2009054933A1|
|Publication number||12287035, 287035, US 2009/0105762 A1, US 2009/105762 A1, US 20090105762 A1, US 20090105762A1, US 2009105762 A1, US 2009105762A1, US-A1-20090105762, US-A1-2009105762, US2009/0105762A1, US2009/105762A1, US20090105762 A1, US20090105762A1, US2009105762 A1, US2009105762A1|
|Inventors||Roger P. Jackson|
|Original Assignee||Jackson Roger P|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (4), Referenced by (4), Classifications (11)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/999,965, filed Oct. 23, 2007 and incorporated by reference herein.
The present invention is directed to dynamic fixation assemblies for use in bone surgery, particularly spinal surgery, and in particular to longitudinal connecting members and cooperating bone anchors or fasteners for such assemblies, the connecting members being attached to at least two bone anchors.
Historically, it has been common to fuse adjacent vertebrae that are placed in fixed relation by the installation therealong of bone screws or other bone anchors and cooperating longitudinal connecting members or other elongate members. Fusion results in the permanent immobilization of one or more of the intervertebral joints. Because the anchoring of bone screws, hooks and other types of anchors directly to a vertebra can result in significant forces being placed on the vertebra, and such forces may ultimately result in the loosening of the bone screw or other anchor from the vertebra, fusion allows for the growth and development of a bone counterpart to the longitudinal connecting member that can maintain the spine in the desired position even if the implants ultimately fail or are removed. Because fusion has been a desired component of spinal stabilization procedures, longitudinal connecting members have been designed that are of a material, size and shape to largely resist flexure, extension, torsion, distraction and compression, and thus substantially immobilize the portion of the spine that is to be fused. Thus, longitudinal connecting members are typically uniform along an entire length thereof, and usually made from a single or integral piece of material having a uniform diameter or width of a size to provide substantially rigid support in all planes.
Fusion, however, has some undesirable side effects. One apparent side effect is the immobilization of a portion of the spine. Furthermore, although fusion may result in a strengthened portion of the spine, it also has been linked to more rapid degeneration and even hyper-mobility and collapse of spinal motion segments that are adjacent to the portion of the spine being fused, reducing or eliminating the ability of such spinal joints to move in a more normal relation to one another. In certain instances, fusion has also failed to provide pain relief.
An alternative to fusion and the use of more rigid longitudinal connecting members or other rigid structure has been a “soft” or “dynamic” stabilization approach in which a flexible loop-, S-, C- or U-shaped member or a coil-like and/or a spring-like member is utilized as an elastic longitudinal connecting member fixed between a pair of pedicle screws in an attempt to create, as much as possible, a normal loading pattern between the vertebrae in flexion, extension, distraction, compression, side bending and torsion. Problems may arise with such devices, however, including tissue scarring, lack of adequate spinal support or being undesirably large or bulky when sized to provide adequate support, and lack of fatigue strength or endurance limit. Fatigue strength has been defined as the repeated loading and unloading of a specific stress on a material structure until it fails. Fatigue strength can be tensile or distraction, compression, shear, torsion, bending, or a combination of these.
Another type of soft or dynamic system known in the art includes bone anchors connected by flexible cords or strands, typically made from a plastic material. Such a cord or strand may be threaded through cannulated spacers that are disposed between adjacent bone anchors when such a cord or strand is implanted, tensioned and attached to the bone anchors. The spacers typically span the distance between bone anchors, providing limits on the bending movement of the cord or strand and thus strengthening and supporting the overall system. Such cord or strand-type systems require specialized bone anchors and tooling for tensioning and holding the cord or strand in the bone anchors. Although flexible, the cords or strands utilized in such systems do not allow for elastic distraction of the system once implanted because the cord or strand must be stretched or pulled to maximum tension in order to provide a stable, supportive system. Also, as currently designed, these systems do not provide any significant torsional resistance.
The complex dynamic conditions associated with spinal movement therefore provide quite a challenge for the design of elongate elastic longitudinal connecting members that exhibit an adequate fatigue strength to provide stabilization and protected motion of the spine, without fusion, and allow for some natural movement of the portion of the spine being reinforced and supported by the elongate elastic or flexible connecting member. A further challenge are situations in which a portion or length of the spine requires a more rigid stabilization, possibly including fusion, while another portion or length may be better supported by a more dynamic system that allows for protective movement.
Longitudinal connecting member assemblies according to the invention for use between at least two bone anchors provide dynamic, protected motion of the spine and may be extended to provide additional dynamic sections or more rigid support along an adjacent length of the spine, with fusion, if desired. A longitudinal connecting member assembly according to the invention has a pair of elongate segments, each segment having at least one and up to a plurality of integral fins extending axially from an end of the segment. The fin or fins of each segment are oriented partially overlapping the fin or fins of the other elongate segment, the fins being spaced from one another. An elastic over-molded outer spacer is disposed about the fins of both segments and holds the segments together in spaced relation. One of the illustrated embodiments further includes an inner floating pin.
Therefore, it is an object of the present invention to overcome one or more of the problems with bone attachment assemblies described above. An object of the invention is to provide dynamic medical implant stabilization assemblies having longitudinal connecting members that include a flexible portion that allows for bending, torsion, compression and distraction of the assembly. A further object of the invention is to provide dynamic medical implant longitudinal connecting members that may be utilized with a variety of bone screws, hooks and other bone anchors. Another object of the invention is to provide a more rigid or solid connecting member portion or segment, if desired, such as a solid rod portion integral to the flexible portion. Additionally, it is an object of the invention to provide a lightweight, reduced volume, low profile assembly including at least two bone anchors and a longitudinal connecting member therebetween. Furthermore, it is an object of the invention to provide apparatus and methods that are easy to use and especially adapted for the intended use thereof and wherein the apparatus are comparatively inexpensive to make and suitable for use.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention.
The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. It is also noted that any reference to the words top, bottom, up and down, and the like, in this application refers to the alignment shown in the various drawings, as well as the normal connotations applied to such devices, and is not intended to restrict positioning of the connecting member assemblies of the application and cooperating bone anchors in actual use.
With reference to
With particular reference to
As best shown in
The dynamic connecting member assembly 1 cooperates with at least a pair of bone anchors, such as the polyaxial bone screws, generally 55 and cooperating closure structures 57 shown in
Because the illustrated end portions 16 and 18 are substantially solid and cylindrical, the connecting member assembly 1 may be used with a wide variety of bone anchors already available for cooperation with rigid rods including fixed, monoaxial bone screws, hinged bone screws, polyaxial bone screws, and bone hooks and the like, with or without compression inserts, that may in turn cooperate with a variety of closure structures having threads, flanges, or other structure for fixing the closure structure to the bone anchor, and may include other features, for example, break-off tops and inner set screws. It is foreseen that the portions 16 and 18 may in other embodiments of the invention have other cross-sectional shapes, including, but not limited to oval, square, rectangular and other curved or polygonal shapes. The bone anchors, closure structures and the connecting member assembly 1 are then operably incorporated in an overall spinal implant system for correcting degenerative conditions, deformities, injuries, or defects to the spinal column of a patient.
The illustrated polyaxial bone screws 55 each include a shank 60 for insertion into a vertebra (not shown), the shank 60 being pivotally attached to an open receiver or head 61. The shank 60 includes a threaded outer surface and may further include a central cannula or through-bore disposed along an axis of rotation of the shank to provide a passage through the shank interior for a length of wire or pin inserted into the vertebra prior to the insertion of the shank 60, the wire or pin providing a guide for insertion of the shank 60 into the vertebra. The receiver 61 has a pair of spaced and generally parallel arms 65 that form an open generally U-shaped channel therebetween that is open at distal ends of the arms 65. The arms 65 each include radially inward or interior surfaces that have a discontinuous guide and advancement structure mateable with cooperating structure on the closure structure 57. The guide and advancement structure may take a variety of forms including a partial helically wound flangeform, a buttress thread, a square thread, a reverse angle thread or other thread like or non-thread like helically wound advancement structure for operably guiding under rotation and advancing the closure structure 57 downward between the receiver arms 65 and having such a nature as to resist splaying of the arms 65 when the closure 57 is advanced into the U-shaped channel. For example, a flange form on the illustrated closure 57 and cooperating structure on the arms 65 is disclosed in Applicant's U.S. Pat. No. 6,726,689, which is incorporated herein by reference.
The shank 60 and the receiver 61 may be attached in a variety of ways. For example, a spline capture connection as described in U.S. Pat. No. 6,716,214, and incorporated by reference herein, is used for the embodiment disclosed herein. Polyaxial bone screws with other types of capture connections may also be used according to the invention, including but not limited to, threaded connections, frictional connections utilizing frusto-conical or polyhedral capture structures, integral top or downloadable shanks, and the like. Also, as indicated above, polyaxial and other bone screws for use with connecting members of the invention may have bone screw shanks that attach directly to the segments 16 and 18 may include compression members or inserts that cooperate with the bone screw shank, receiver and closure structure to secure the connecting member assembly to the bone screw and/or fix the bone screw shank at a desired angle with respect to the bone screw receiver that holds the longitudinal connecting member assembly. Furthermore, although the closure structure 57 of the present invention is illustrated with the polyaxial bone screw 55 having an open receiver or head 61, it foreseen that a variety of closure structure may be used in conjunction with any type of medical implant having an open or closed head, including monoaxial bone screws, hinged bone screws, hooks and the like used in spinal surgery.
To provide a biologically active interface with the bone, the threaded shank 60 may be coated, perforated, made porous or otherwise treated. The treatment may include, but is not limited to a plasma spray coating or other type of coating of a metal or, for example, a calcium phosphate; or a roughening, perforation or indentation in the shank surface, such as by sputtering, sand blasting or acid etching, that allows for bony ingrowth or ongrowth. Certain metal coatings act as a scaffold for bone ingrowth. Bio-ceramic calcium phosphate coatings include, but are not limited to: alpha-tri-calcium phosphate and beta-tri-calcium phosphate (Ca3 (PO4)2, tetra-calcium phosphate (Ca4P2O9), amorphous calcium phosphate and hydroxyapatite (Ca10(PO4)6(OH)2). Coating with hydroxyapatite, for example, is desirable as hydroxyapatite is chemically similar to bone with respect to mineral content and has been identified as being bioactive and thus not only supportive of bone ingrowth, but actively taking part in bone bonding.
The longitudinal connecting member assembly 1 illustrated in
Specifically, in the illustrated embodiment, the pin 8 and the end portions 16 and 18 are all substantially solid, smooth and uniform cylinders or rods, each of a uniform circular cross-section. It is foreseen that in some embodiments, the pin 8 and the segments 4 and 5 may include a small central lumen along an entire length thereof and opening at each end thereof to allow for threading therethrough and subsequent percutaneous implantation of the member 1. The illustrated pin 8 has an end 72 and an opposite end 74, with the solid end portion 16 terminating at an end 76 and the solid end portion 18 terminating at an end 78. The portions 16 and 18 are each sized and shaped to be received in the channel formed between the arms 65 of a bone screw 55 with the plates 20 and 22 and the molded spacer 10 disposed between cooperating bone screws 55.
As shown in
The spacer 10 advantageously cooperates with the plates 20 and 22, the fins 24 and 26 and the pin 8 to provide a flexible or dynamic segment that allows for bending, torsion, compression and distraction of the assembly 1. The spacer 10 further provides a smooth substantially cylindrical surface that protects a patient's body tissue from damage that might otherwise occur with, for example, a spring-like dynamic member.
In the embodiment shown, the molded spacer 10 is fabricated about the plates 20 and 22 and the fins 24 and 26, as will be described more fully below, and in the presence of the pin 8, with molded plastic flowing about the plates, pin and fins. The formed elastomer is substantially cylindrical in outer form with an external substantially cylindrical surface 84 that has the same or substantially similar diameter as the diameter of the outer cylindrical surfaces 36 and 38 of the respective stop plates 20 and 22. It is foreseen that in some embodiments, the spacer may be molded to be of square, rectangular or other outer and inner cross-sections including curved or polygonal shapes. The spacer 10 may further include one or more compression grooves (not shown) formed in the surface 84. During the molding process a sleeve or other material (not shown) may be placed about the pin 8 so that the spacer 10 has in internal surface of a slightly greater diameter than an outer diameter of the pin 8, allowing for axially directed sliding movement of the spacer 10 with respect to the pin 8.
As stated above, it is foreseen that in other embodiments of the invention, the pin 8 may be omitted, resulting in a more flexible assembly 1. The pin 8 may be replaced with tensioned or un-tensioned cords or cables that are affixed to one or both of the segments 4 and 5. The pin 8 may be made from an elastomer. The pin 8 may be fixed to one of the segments 4 or 5 and/or extend through the other segment, providing an elongate inner core extending along a substantial length of the assembly, that may be pre-tensioned, if desired. In such embodiments, elastomeric end bumpers may be added to the assembly. The fins 24 and 26 may also be modified. For example, fewer, thicker fins may be utilized or a greater number of thinner fins may be used. Fewer fins may desirably allow for more torsional play in the assembly 1, whereas a greater number of fins may result in a tighter, less flexible assembly with the fins abutting one another when under fairly small torsional loads. In other embodiments, the fins may be solid and not include the c-shaped surface, allowing for more flexibility in distraction and compression. The fins may also have central opening or fenestrations.
With reference to
In use, at least two bone screws 55 are implanted into vertebrae for use with the longitudinal connecting member assembly 1. Each vertebra may be pre-drilled to minimize stressing the bone. Furthermore, when a cannulated bone screw shank is utilized, each vertebra will have a guide wire or pin (not shown) inserted therein that is shaped for the bone screw cannula of the bone screw shank 60 and provides a guide for the placement and angle of the shank 60 with respect to the cooperating vertebra. A further tap hole may be made and the shank 60 is then driven into the vertebra by rotation of a driving tool (not shown) that engages a driving feature at or near a top of the shank 60. It is foreseen that the screws 55 and the longitudinal connecting member 1 can be inserted in a percutaneous or minimally invasive surgical manner.
With particular reference to
With reference to
The assembly 1 is thus substantially dynamically loaded and oriented relative to the cooperating vertebra, providing relief (e.g., shock absorption) and protected movement with respect to flexion, extension, distraction, compressive, torsion and shear forces placed on the assembly 1 and the two connected bone screws 55. The spacer 10 and cooperating pin 8 and fins 24 and 26 allows the assembly 1 to twist or turn, providing some relief for torsional stresses. The spacer 10 in cooperation with the fins 24 and 26, however limits such torsional movement as well as bending movement, compression and distraction, providing spinal support. The pin 8 further provides protection against sheer stresses placed on the assembly 1.
If removal of the assembly 1 from any of the bone screw assemblies 55 is necessary, or if it is desired to release the assembly 1 at a particular location, disassembly is accomplished by using the driving tool (not shown) with a driving formation cooperating with the closure structure 57 internal drive 96 to rotate and remove the closure structure 57 from the receiver 61. Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly.
Eventually, if the spine requires more rigid support, the connecting member assembly 1 according to the invention may be removed and replaced with another longitudinal connecting member, such as a solid rod, having the same diameter as the end portions 16 and 18, utilizing the same receivers 61 and the same or similar closure structures 57. Alternatively, if less support is eventually required, a less rigid, more flexible assembly, for example, an assembly 1 made without the pin 8 or from a more flexible material, or with fewer fins, but with end portions having the same diameter as the portions 16 and 18, may replace the assembly 1, also utilizing the same bone screws 55.
With reference to
The dynamic connecting member assembly 101 cooperates with at least a pair of bone anchors, such as the polyaxial bone screws, generally 55 and cooperating closure structures 57 shown in
The spacer 110 advantageously cooperates with the plates 120 and 122 and the fins 124 and 126 to provide a flexible or dynamic segment that allows for bending, torsion, compression and distraction of the assembly 101. The spacer 110 further provides a smooth substantially cylindrical surface that protects a patient's body tissue from damage that might otherwise occur with, for example, a spring-like dynamic member. In the embodiment shown, the molded spacer 110 is fabricated about the plates 120 and 122, the fins 124 and 126 and between respective end surfaces 180 and 182 of central supports 132 and 134. The formed elastomer is substantially cylindrical in outer form with an external substantially cylindrical surface 184 that has the same or slightly larger diameter as the diameter of the outer cylindrical surfaces 136 and 138 of the respective stop plates 120 and 122. It is foreseen that in some embodiments, the spacer may be molded to be of square, rectangular or other outer and inner cross-sections including curved or polygonal shapes. The spacer 110 may further include one or more compression grooves (not shown) formed in the surface 184.
In such embodiments, elastomeric end bumpers may be added to the assembly. The fins 124 and 126 may also be modified. For example, fewer, thicker fins may be utilized or a greater number of thinner fins may be used. Fewer fins may desirably allow for more torsional play in the assembly 101, whereas a greater number of fins may result in a tighter, less flexible assembly with the fins abutting one another when under fairly small torsional loads. In other embodiments, the fins may be solid and not include the c-shaped surface, allowing for more flexibility in distraction and compression. The fins may also have central opening or fenestrations.
The longitudinal connecting member assembly 101 is assembled by facing the end surfaces 180 and 182 towards one another and moving the fins 124 and 126 into slightly overlapping position with respect to the axis AA and in evenly spaced radial relation. This is performed in a factory setting with the end portions 116 and 118 held in a jig or other holding mechanism that frictionally engages and holds the sections 116 and 118, for example, and the spacer 110 is molded about the plates 120 and 122 as well as the fins 124 and 126 as shown in phantom in
The assembly 101 is eventually positioned in an open or percutaneous manner in cooperation with the at least two bone screws 55 with the spacer 110 disposed between the two bone screws 55 and the end portions 116 and 118 each within the U-shaped channels of the two bone screws 55. A closure structure 57 is then inserted into and advanced between the arms 65 of each of the bone screws 55. The closure structure 57 is rotated, using a tool (not shown) engaged with the inner drive 96 until a selected pressure is reached at which point the portion 116 or 118 is urged toward, but not completely seated in the U-shaped channels of the bone screws 55. For example, about 80 to about 120 inch pounds pressure may be required for fixing the bone screw shank 60 with respect to the receiver 61 at a desired angle of articulation.
The assembly 101 is thus substantially dynamically loaded and oriented relative to the cooperating vertebra, providing relief (e.g., shock absorption) and protected movement with respect to flexion, extension, distraction, compressive, torsion and shear forces placed on the assembly 101 and the two connected bone screws 55. The spacer 110 in cooperation with the fins 124 and 126 limits torsional movement as well as bending movement, compression and distraction, providing spinal support.
If removal of the assembly 101 from any of the bone screw assemblies 55 is necessary, or if it is desired to release the assembly 101 at a particular location, disassembly is accomplished by using the driving tool (not shown) with a driving formation cooperating with the closure structure 57 internal drive 96 to rotate and remove the closure structure 57 from the receiver 61. Disassembly is then accomplished in reverse order to the procedure described previously herein for assembly.
It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.
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|U.S. Classification||606/246, 623/17.11|
|International Classification||A61B17/70, A61F2/44|
|Cooperative Classification||A61B17/7037, A61B17/7025, A61B17/7031, A61B17/7004|
|European Classification||A61B17/70B1R8, A61B17/70B1R12, A61B17/70B1C|